Electrical conductor



NOV- 19, 1940- w. c. ROBINSON ETAL I 2,222,556

ELECTRICAL CONDUCTOR Filed Aug. 18, 1959 y INVENTORS MMM www, Mx

, gM//MW Patented Nov. 19, 1940 ELECTRICAL CONDUCTR William C. Robinson, Sewiclxley, Pa., and Ralph W. E. Moore, Riverdale, N. Y., assignors to National Electric Products Corporation, a core poration of Delaware Application August 18,

3 Claims.

This invention ductor.

We have discovered that in the manufacture of insulated conductors great advantage is derived both in the manufacture and also in the qualities and useful life of an insulated conductor by replacing the braided or Woven fibrous covering which previously hasbeen commonly applied around the core of the conductor by a serving of fibrous material, such as cotton strand, wound on 'the conductor core in a simple helical lay with its turns ln intimate contact with each other, and bound together against opening tendencies during the dexion of a conductor by a binder lament or laments. Further we have discovered that if the binder lament or lilaments, which are laid in a helix opposite in sense to the helical lay of the absorbent strands, are laid to form a suiciently great angle With respect to the longitudinal axis of the conductor, or with respect to the angle at which the served covering is laid, the binder filament, though ci commonly used material and much lighter in gauge than the serving strands, tends remarkably well to resist breakage under severe ilexion oi the conductor. These discoveries we have disclosed and claimed in our co-pending applim cations Serial No. 181,910, iiled December 27. 1937, and Serial No. 224,522, led August l2, i938; or which applications this forms a continuation-in-nart.

We have further discovered that great advan tage is to be derived in the insulated conductor assembly by using a binder filament having an extensibility greatly exceeding the extensibility of cotton, and which because of such extensibility, coupled with superior strength, simplifies the manufacture and improves the qualities of the insulated conductor as a Whole.

It should be eyplained that in an insulated conductor in which the brous covering or" the conductor core is served, there is a strong tendency for the turns of the serving to open up by separation from each other under severe ilexion, or kinking, oi the conductor. When the turns so open up, the continuity of the moisture-resistant and arne-retardant material with which they are saturated is broken, and the encapsulation provided by the overlying coating of such material and any further coatings, such as coating of paint and wax, is also broken. The pro.- tective effect of the fibrous covering of the conductor core is thus destroyed, since air and moisture may penetrate into the interior of the conductor structure in the region of the disintegrarelates to an insulated con- 1939, Seriali No, 296,852

tion, and the flame-retardant elements of the structure are interrupted. This in the past has proven obstructive to the practice of serving absorbent material around the inner elements, or core, of insulated conductors, although a simple serving tends, to form a better seal when impregnated with a viscous saturant, and thus provides a covering less pervious to the entry of air or moisture and of better insulating qualities than does a braided covering. Also it does not tend, as does a braid, to entrap air, the presence of which in contact with a rubber sheath in a conductor tends ultimately to cause deterioration of the rubber.

It is the opening tendency between the turns of a served covering or wrap which a binder lament prevents, and the integration of the insulating structure is thus no greater than the eiiectiveness oi the binder. It may be noted that even in insulated conductors which comprise two coverings or wraps served oppositely to each othenan opening between the turns of the outer wrap when the conductor is severely flexed, or lrinled, serves to disintegrate the insulating structure oi the conductor, and a suitably organized binder filament is nonetheless essential to counteract such opening tendency.

With the above explanation, it will be readily understood that in an insulated conductor in which dependence is placed upon a served and bound fibrous covering, rather than upon a fibrous covering which is braided or woven, the assembly as a whole eiectivelypossesses an endurance as an adequately insulated conductive assembly directly dependent upon the ability of the binder lainent enduringly to lock in close contact with each other the turns of the served wrap, or the outermost served wrap, of the conductor assembly.

n the accompanying drawing Fig. I is a plan View or elevation of the interior assembly of an insulated conductor made in accordance with the structural arrangement of which our invention is incorporated; this ligure of the drawings showing a conductor of relatively small size, such as a conductor smaller than a No. 6 size. Fig. II is a generally similar View which, however, shows the internal assembly of a conductor, of a No. 6 size, or greater. Fig. III is a View of a completed insulated conductor including the internal assembly shown in Fig. I, the conductor being shown partly in elevation or plan view or partly in central longitudinal section. Fig. IV is a fragmentary central longitudinal sectional view of the conductor assembly shown in Fig. I,

illustrating the structure on an enlarged scale. Fig. V is a cross-sectional view through the conductor shown in Fig. IV.

In Figl I of the drawing, reference numeral I designates the metallic conductive element of the conductor assembly. This conductive element i is shown as a single wire of copper, or the like, but may, if desired, be a conductive element of the stranded sort known 'to the trade as a ilexible conductor. 'I'he metallic conductive element I is, as shown, surrounded directly by a one-piece sheath 2 of rubber, or rubber composition, and this innermost assembly of metallic conductive element or sheath is usually termed the core of the conductor consistently with our invention, this core may consist of the metallic conductive element covered with an impregnated braid or other material, or may consist merely of the metallic conductive element itself. There is helically wound or served a wrap of absorbent fibrous material, such as cotton strands. This wrap or serving 3 is shown in Figs. I and II as being served with the simultaneous application of eight ends or individual strands, the more rapidly to eii'ect the serving. Also, the more rapidly to eect the serving and the more coherently to apply the wrap, the strands are served with a substantial lead, being shown as applied at an angle a of about 50 degrees to the longitudinal axis of the conductor.

The binder nlament 4 is applied wholly outside the serving l and is laid in a helix opposite to that in which the serving is laid, so that the turns of the open binder structure cross, and bind together, the turns of the serving. As above explained, the function of this open binder structure is to bind the turns of the serving against a separation from each other which would destroy the integration of the insulating and protective assembly outwardly of the core, and in order to perform this function, it is necessary that the binder lament (by which term we intend to include any number of filaments which form an open structure) should itself remain intact. To

I this end the binder nlament is laid to form with the longitudinal axis of the conductor an angle b greater than the angle a formed therewith by the strands of the serving. As shown, angle b is approximately 65 degrees. ,K

In Figs. III, IV and V of the drawing there is shown a complete conductor assembly in which the wrap 3, and binder structure I, are shown as saturated with and embedded in an envelope l of viscous saturant, such as the pitchy moistureresistant and llame-retardant material commonly used in making insulated conductors. In addition to this encapsulation of the viscous material, there are -other layers of encapsulating material, such as paint and wax, which are designated by reference numerals I and 1.

Considering the iigures of the drawing, it will be apparent how a separation of the served turns of the wrap, by breaking through the encapsulating coatings of the conductor and interrupting the cohesion of the wrap, exposes the rubber sheath 2 to deteriorating agencies, and will allow moisture to work into the interior of they conductor structure. It will similarly be apparent n ot only why the short lead of the binder helix is of advantage in lessening elongation of the binder, but also how a binder of suiiicient strength may continue to oppose the opening tendency by the turns of the served wrap during severe iiexion by continuing to exert its binding forceasareactiontotheforcedincreaseinits length which exion causes. That is, we have discovered that the yielding oi' the binder to flexion, by its elongation, does not temporarily so negative its binding eifect as to permit the opening between turns of the wrap which must be prevented.

It has been indicated that in order to obtain maximum life and utility of the insulated conductor, the angle or lead of the binder structure is of importance in protecting the binder structure against severe flexion. In smaller size conductors, such as the conductor shown in Fig. I of the drawing, more abrupt ilexion angles are usually encountered, but with the larger size conductors, the eii'ect of flexion is proportionally greater, and this is particularly true in those turns of a large size conductor, which is so closely coiled as to be subjected to an elongating eifect throughout a relatively great length of its binder helix. In Fig. II, therefore, the served wrap la surroundingthe conductor core has its strands or turns bound together by a nlamentary binder structure 4a laid at an angle of approximately 70 degrees to the longitudinal axis of the conductor.

We have made an additional discovery'which in the insulated binder assembly is one of substantial importance. It is, that in the assembly the security of integration depends not only in the presence of the binder lament, but in the extensibility of that filament as applied to the served wrapping which by1 its binding eilect the binder structure maintains in coherent condition. Thus, if the binder nlament be made of cotton, as is conventional there is in severe flexion of the conductor a frequently destructive tendency to disrupt the binder at some point in its helical structure at which the` forces tending to elongate the material of the helix exceed the ability of the material to elongate. As explained above, the angle at which the` helical turns of the binder structure are laid is of importance'in modifying that tendency. We have found that if the helix of the open binder structure be of adequate extensibility, the binder structure may be greatly elongated without losing its effectiveness by a loosening of its turns. That is, being able to resist rupture because of its extensibility and strength, it is enabled progressively so to react against the elongating forces that it continues eifectively to bind the turns of the serving to each other.

Taking as a standard for use specifically as binder filaments in the described assembly, the various lamented cellulose esters known generically by the trade name Rayon, and the filamented fiber-forming high-molecular-weight polyamides known by the tradename Nylon" and vdisclosed in United States Patents to Wallace H. Carothers No. 2,130,947 and No. 2,130,948, we have found that such materials exemplary of those whose inherent viscosity permits them to be extruded into long individually strong and elastic.

ilbers, have an extensibility. or elongation, and elastic recovery greatly exceeding that of cotton. For example, the extensibility or elongation of the cellulose ester filaments is approximately three times that of a high grade cotton filament, coupled with a strength twice that of the cotton filament. The polyamide filaments have an extensibility, or elongation, about four times that of a corresponding cotton filament coupled with a strength about twice that of the cotton nlament. In these exemplary materials extensibility and strength are coupled, and we have found that when used in an insulated conductor assemassauts bly as an open binder structure; such as the binder l, filaments of this sort-retain their effectiveness in binding the served wrap both during and following severe elongation. This is in distinction from cotton which ruptures when its ability to elongate is quickly exhausted, and other materials which, while possessing marked extensibility, lose their. ability to sustain loads when Ielongated.

In evaluating the benefit of extensibility in the open binder structure of a conductor organized as herein shown, in terms of improvement in the conductor assembly, we may say that a more specialized binder filament does not lead to striking improvement in the conductor assembly unless it has an extensibility greatly exceeding that of a similar binder structure made of the conventional cotton lament, and couples this with a strength greater than that of a binder structure made of cotton filament, This, because the advantages derived from extensibility, does not progressively occur with increase in extensibility. Whereas the elongation in the conductor assembly may be'effective throughout a relatively great length of the conductor, it may be wholly localized, so that by a relatively short length of the binder filament is called upon to endure the forces tending by elongation to rupture it. We can, therefore. say that to obtain substantial benefit in the conductor structure as a whole from the selective inclusion of an extensible binder filament, the binder filament must have a comparative extensibility almost twice that of the conventional cotton, and preferably should have an extensibility as great as that of rayon.

The materials herein identified as Rayon and Nylon do not have an origin in common. Both may be considered as synthetic silk-like fibrous materials, although Rayon" is derived from cellulose, and Nylon is produced by reacting diamines with (li-carboxylic acids or amine-forming derivatives of dibasic carboxylic acid. They are representatives of a class of filamentary materials of like character, which also possess in common the quality of extensibility in high order and relatively great strength.

We claim as our invention: A

1. An electrical conductor assembly comprising an electrically insulated vinner conductive structure and an outer protective jacket therefore in the form of a helical serving of highly absorbent and relatively inelastic thread laid in close turns with a substantial lead and without overlap, to give approximately complete coverage ,and an effective saturant-absorbing assembly, in combination with an open locking structure composed of a filament of plastic material which is substantially less absorbent and A substantially stronger and more elastic than the thread of the absorbent jacket, said filament being wound upon the said absorbent jacket oppositely to the winding thereof and at a substantial angle with the conductor axis and with its turns so spaced as to expose the greater part of said jacket.

2. An electrical conductor assembly in accordance with claim 1 in which the relatively strong and elastic locking filament of the assem bly is a filament selected from the fiber-forming cellulose esters.

3. An electrical conductor assembly in accordance with claim 1 in which the relatively strong and elastic locking filament of the assembly is composed of iilamented berforming super-polyamides.

WILLIAM C. ROBINSON. RALPH W. E. MOORE. 

